Multiple-input multiple-output (MIMO) antennas may suffer from mutual coupling. Mutual coupling may degrade both the signal-to-interference-noise ratio (SINR) of an antenna array and the convergence of the array's signal processing algorithms. Further, mutual coupling may degrade the estimations of carrier frequency offset, channel estimation, angle of arrival, error rate and capacity of a MIMO antenna. Due to the random phase excitations at the antenna ports during transmission by a MIMO antenna, mutual coupling may also have an adverse effect on the active voltage standing wave ratio (VSWR).
Wireless communication products utilizing MIMO antenna arrays may place upper and lower bounds on the space that may be occupied by a MIMO antenna. The typically compact nature of this space leads to the radiating elements of a MIMO antenna being located in close proximity to one another, which may satisfy the compactness requirements, but at the cost of performance degradation as a result of the effects of mutual coupling which are only heightened by the close proximity of the radiating elements.
In an effort to mitigate mutual coupling, MIMO pre-coding and decoding schemes have been implemented. However, the output SINR of an adaptive MIMO antenna array cannot be improved by compensating for the mutual coupling only during the post-processing stage. Various diversity techniques, such as space diversity, polarization diversity and pattern diversity, have also been utilized to address the degradation in antenna performance brought about by mutual coupling. However, these various diversity techniques also have generally been of only limited usefulness in controlling the adverse effects of mutual coupling.